The present invention concerns a devices for the pseudo-analog display of the value of a physical parameter.
Conventional analog devices which are intended to display the value of a physical parameter generally comprise a hand or pointer which is mounted on a pivot. The hand or pointer is driven in rotation by a suitable mechanism and occupies an angular position corresponding to the value to be displayed, which can be read, opposite the hand or pointer, on a fixed graduated scale. In a first approximation, any variation in the value of the physical parameter, however small it may be, causes a corresponding variation in the position of the hand or pointer.
On the other hand, in pseudo-analog display devices the hand or pointer, or the member which takes the place thereof, can occupy only a given number of different positions. The value of the physical parameter measured must therefore vary at least by a given quantity in order for the displayed value to be changed. If necessary, the number of different positions on the display may be relatively high and minimum detectable variation can be relatively small so that the movements of the hand or pointer in dependence on the variations in the physical parameter are apparently continuous.
This type of display device which is well known generally comprises a circuit for producing a numerical signal whose value is representative of the value of the physical parameter. When the physical parameter is for example a pressure, a speed, etc., the circuit comprises a detector which produces an electrical signal representative of the value of the physical parameter, and an analog-to-digital converter. The latter produces the numerical signal representative of the value of the physical parameter, for example in binary form.
When the physical parameter is time, the numerical signal can be produced by a counting chain connected to a time base circuit.
In all cases, the numerical signal is applied to a code converter circuit which controls a pseudo-analog display cell, possibly by way of an amplifier circuit.
Such a display cell comprises display elements which are disposed one beside the other and the total number of which is equal to the number of values that may be assumed by the numerical signal.
The code converter and the display cell are so arranged that, for each of the values of the numerical signal, one and only one of the display elements is activated, that is to say, made visible.
The display elements are generally of such a shape that they resemble the pointer of a conventional display and a fixed scale is disposed in relation therewith so that the user of the device can read the corresponding value of the physical parameter, opposite the activated element.
The display cell may use light-emitting diodes (LED), a liquid crystal, an electrochromic material, or any other means.
When the physical parameter to be measured is a voltage, current, speed, pressure, etc., the display elements are generally disposed in a line, which may be straight or curved, like the graduations of a conventional analog display.
When the physical parameter to be measured is time, the display elements are generally disposed in a ring so that the last element is adjacent to the first element, like the arrangement of the graduations on the dial of a watch.
U.S. Pat. No. 3,987,617 in particular proposes a pseudo-analog display cell of the latter type, comprising twenty four display elements for displaying hours (in half-hours), sixty elements for displaying minutes, and as many for seconds. A display device using this kind of cell however suffers from poor legibility due to the small surface area of the display elements, in particular those used for displaying minutes. In addition, the production cost of a device of this type increases as the cell requires a greater number of external connections for connection to its control circuit.